Mice placed in the center of an apparatus, the Elevated-Plus Maze, can choose to enter one of two types of alleys (or arms), an open alley or a closed alley, both of which are elevated significantly above the floor. This behavior can be quantified as the percentage of times an animal enters the open alley in comparison to the total number of entries into either the open or closed arms (%OpenArmEntries). %OpenArmEntries is assumed to reflect the balance between an animal's drive to explore new areas and the fear (or anxiety) engendered by being in an open relatively more lit area An F2 generation of animals was produced from two inbred strains, A/J and CBA/J, that differed widely in their Elevated Plus-Maze behavior. The behavior of 228 of these animals was measured, and DNA prepared from 160 animals. The F2 progeny displayed a broad range of behavior in the Elevated Plus-Maze with some animals behaving in an identical manner as the original inbred A/J and CBA/J strains. Genotyping was performed using microsatellite primers and PCR. Using QTL analysis a single locus was found that explained 16% of the total behavioral variance with respect to the percentage of entries each animal made to the open arms. We have created a second F2 generation, beginning with new members of the same inbred strains to confirm the above findings. Our initial results confirm our earlier findings.